General purpose shipping containers are the fundamental type from which all other shipping containers are derived. These containers are built for intermodal transportation of goods via ship, barge, train, air, and truck, without the need to unload or reload their cargo.
About 90% of the global inventory of containers are the so-called dry freight or general purpose containers. They go by a number of names including container, freight container, cargo container, shipping container, ISO container, sea container, Conex box, ocean container, container van, or sea can. 80% of these general purpose shipping containers are the 20ft (6 meter) and 40ft (12 meter) lengths. While these two lengths dominate, shipping containers come in a variety of lengths, from 8ft (2.4 meters) up to as long as 56ft (17 meters). There also two heights available: standard, which is 8ft 6in (2.6 meters) and high cube, at 9ft 6in (2.9 meters) tall.
The purpose of these containers is to transport cargo and goods in larger, unitized loads that can be easily handled. Shipping containers are designed to be moved and stacked in tight spaces, such as onboard a ship or in a yard.
Containers must be built to specifications that meet the stresses and strains of intermodal shipping. To that end, most containers are rectangular, closed box models, with doors on one end. They are made with corrugated weathering steel, also known as Corten®, which is produced by US Steel. This alloy contains copper, chromium, and nickel. As the steel weathers, these metals create a layer of insoluble compounds that protects the steel underneath.
During manufacturing, each container begins with the base. This is comprised of two long rails and two end pieces made out of high tensile steel. Crossmembers are inserted between the long rails and welded in place. While the base is being assembled and welded, the front, back, doors, side panels, and roof are also being fabricated. All completed components are then staged in the final assembly area where each piece is set so workers can weld them together. All welds throughout the process must meet rigorous quality standards to ensure the container can withstand the real-world stresses of intermodal transportation.
After final assembly of the steel components is complete, prepped and painted, a heavy-duty, treated plywood floor is installed, using self-tapping screws to secure it to the crossmembers underneath. This kind of flooring is somewhat slip-resistant and much easier to maintain than a steel floor.
Each container has castings at the top and bottom of the corner posts that make it possible to stack and lock the containers together. To ensure safe, stable stacking, there are rules that must be followed. Shipping containers longer than 20ft (6 meters), can be stacked on the 20ft (6 meter) containers, so long as there are two in a row, but 20ft (6 meter) containers can never be stacked on longer containers. All containers longer than 40ft (12 meters) stack at the 40ft (12 meter) coupling width.
Containers are transferred using a variety of equipment, including cranes, reach stackers, forklifts, and straddle carriers. ISO standard containers can be lifted and handled in a variety of ways by their corner fixtures, but the 45ft (13.7 meters) type-E containers have limits on how they can be lifted and handled.
Security and Load Securement
A variety of materials and means are utilized to safely secure cargo inside of containers. Polyester strapping, dunnage bags, wood blocks, and other items are used to stabilize cargo against shifting and movement during transport. For high-value cargo, containers are equipped with a panel and various alarm systems, including a radio signal that can alert security guards if a container is broken into. Currently, there are new technologies being developed to further improve high value cargo security including laser-etched seals, tamper-evident seals with RFID and real-time GPS location, along with changes in logistics planning to make it much more difficult for thieves to steal loads through the use of forged seals and documents.
Power generators, water treatments systems, and other specialized systems can be built inside of containers for portability and ease of movement. The United States military has been using shipping containers in one form or another since WWII to transport everything from weapons and ammunition to radio communications equipment, food and supplies, and power generation stations.
Creative use of containers is a long-standing practice, the most common of which is storage. Containers no longer used for transportation of goods are ready-made storage units, and can be used almost anywhere. In recent years, another trend has emerged, with people building homes out of used shipping containers, which is environmentally friendly and cost-effective. People have made a variety of buildings out of shipping containers, including cafes, shops, mobile data centers, and man caves. When it comes to repurposing, there is no limit to what a person can do with a used shipping container. While there may be no limit to the possibilities for containers, there are some limitations to how containers can be used. When using them to build a multi-level home, it is important they have the proper structural support. Failure to do this could result in catastrophic failure, causing part of the home to collapse. Also, while the sides of a container are designed to withstand the stresses of oceangoing passage, they are not suitable for subterranean installation. The sides are not designed to withstand the lateral forces of soil pushing against them, making a container vulnerable to collapse. The same goes for the roof. If a container were buried in the ground, the roof would likely give way, unable to support the weight of the soil on top of it. The takeaway from all this is to thoroughly research the structural limitations of shipping containers before using them to build anything.
How Shipping Containers Became the Best Way to Ship Cargo
Before Malcolm McLean came along, there was no standardization. The containers that existed were made in every imaginable shape and size, often causing as many problems as they attempted to solve. With McLean’s vision of standardizing shipping container dimensions and securement, it became possible to outfit ships, trains, and trucks for ease of transfer and handling of these containers. Today, it is still the most efficient means of moving any cargo that can be bundled, baled, stacked on pallets, or loaded loose in bulk.
As more shippers find ways to utilize containers for shipment of their goods, break bulk cargo will continue its decline, improving shipping efficiency while reducing costs. Emerging technologies are being utilized to make shipments more secure from theft, and allow shippers to track their cargo in real time from origin to final destination.